1. Field of the Invention
The present invention generally relates to generalized virtual inspectors.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Automated surface inspection is important to a number of different fields. For instance, inspection is substantially important when fabricating semiconductors to improve yields and provide process control. Surface inspection is particularly challenging for semiconductor wafers in that the dimensions of structures present on the surface are extremely small and are continuously getting smaller as technology progresses. The size of the structures requires inspection systems to have extremely high resolution, which in turn translates to a substantially large amount of data collected during the inspection process. For example, the inspection of a single 300 mm diameter water may generate in excess of 15 terapixels of image data collected in less than 60 minutes when using current inspection systems such as the 29xx system, which is commercially available from KLA-Tencor, Milpitas, Calif.
Because of the enormous amount of data generated by inspection, common practice is to design wafer inspection systems so that they process the acquired data rapidly since storing this amount of data would be either substantially expensive or practically impossible due to the underlying limitations of the technology used in the computers implementing the inspection algorithms. For example, current wafer inspection systems may utilize multiple processors (called nodes) with dedicated memory in each to distribute the computation toad required to handle data streaming in from a sensor. This data may be partitioned into swaths across the wafer, and the swaths may be further sub-divided into sub-swaths, each sub-swath being processed by one node. The results of computation are passed to a host computer, and the memory of each node is cleared to make way for the data for the next (sub) swath. No “state” information about the previous scan is retained. In other words, the data from the sensor is discarded when the node reaches the end of the swath. As such, the node has no memory across scans.
Therefore, due to the large amount of data acquired, most wafer inspection has been implemented by providing image processing equipment capable of executing a defect detection algorithm at speeds matching those of the data acquisition apparatus. Executing the defect detection algorithm at such speeds often limits the complexity of the algorithm used. In particular, relatively simple algorithms may be used to ensure that the data is processed as fast as it is acquired. Alternatively, more complex defect detection algorithms that process data slower than the data acquisition rate may be used, but such algorithms require slower data acquisition thereby reducing the overall throughput of the inspection system.
Accordingly, it would be advantageous to develop systems and methods for creating persistent data for a wafer and using persistent data for inspection-related functions.